Farmers from around the world who till and plant row crops on sloping, highly erodible land have been seeking for many years a method of efficiently tilling and planting row crops that will restrict waterborne soil erosion from present high levels. Severe waterborne soil erosion results in the loss of soil, as well as the loss of small corn or soybean plants if the soil erosion occurs in May or June. This erosion can result in a significant loss of crop production.
A problem coincidental with erosion is crop residue loss. Crop residue floats on water so when highly erodible land receives heavy rainfall any unattached crop residue on the surface is free to float away with the rainwater runoff.
This process is demonstrated by checking a flood control dam installed across a gully between hillsides of highly erodible land after a heavy rainfall. If these hillsides were previously planted with a row crop, such as corn, the rainwater runoff collected will be soil laden and a brown color. This rainwater will also have up to a 2 -inch thick layer of crop residue floating on the surface. Woven wire fences in the path of the rainwater runoff are also good places to check for crop residue loss. This crop residue loss process lowers the potential organic material content and fertility of the soil in that area.
Soil experts have proven that rain drops pounding on bare soil during rainstorms break up the surface of the soil into very fine particles. These fine particles of soil called silt are carried into every fissure and opening in the surface of the soil and decrease the percolation rate of rainwater into the soil. Tests run by soil scientists indicate that this silting process may reduce the percolation rate of rainwater into the soil by as much as fifty percent. Soil experts use the following guidelines for predicting rainwater percolation rates by area across the midwestern U.S. The percolation rate is about one-half inch per hour if trash is present close to the top or on top of the soil surface in the heavy dark soils of eastern Iowa, Ill., Ind., and Ohio. The percolation rate is about one inch per hour into the lighter soils of western Iowa, Miss., Nebr., and Kans. A system of farming called minimum tillage has developed around the concept of leaving the trash on the soil surface. This system works well on level or slightly sloped land as long as the rainfall rates stay below the percolation rates of rainwater into the soil. When heavy rainfall exceeds the percolation rate of rainwater into the soil or prolonged rainfalls saturate the topsoil, then heavy soil erosion occurs. Rainfall rates up to four and one-fourth inches in twenty minutes have been observed in western Iowa. Tons of topsoil and crop residue left with the runoff rainwater. Probably less than one-half inch of this rainfall actually percolated into the soil. The soil moisture needed to help the farmer raise full crops ran off to the local streams and rivers.
To date the standard answer to limit soil erosion has been to limit slope length to one hundred twenty feet. This is currently done by installing large, parallel terraces across long slopes. The terraces are positioned one hundred twenty feet apart starting near the top of the slope and moving toward the bottom. The height of these terraces depends on local rainfall conditions, and most are sized for two to three inches of rainfall per hour. Lateral dams are also sometimes provided to keep rainwater from running to a low spot above the terrace. Occasionally drainpipe systems are also used to carry excess rainwater to the bottom of the slope. Using this parallel terrace system, waterborne soil eroded during very heavy rainfall is collected on the top side of these terraces. This soil erosion generally limits the life of these terraces to about ten years. After ten years of use most terrace systems will run over during heavy rainfall if the accumulated silt isn't removed. Very heavy rainfalls are often during or followed by long dry periods when excess rainwater that was allowed to runoff is needed to grow the row crop planted on this sloping land. When large terraces are used the accumulated water from the area above the terrace is trapped and allowed to infiltrate into the soil immediately above the terrace and the terrace itself. This excess water and silt in a small area can cover one or two rows in the bottom of the terrace with silt, but four to six rows that are in the reservoir area of the terrace will do very well in a following dry period.
Many farmers have not installed these large terraces on highly erodible land over the years, even with government assistance, due to a number of reasons such as:
1. The large terraces remove acres of productive farm land from use. PA1 2. The large terraces cost thousands of dollars to install and more thousands of dollars to remove the silt in the future. PA1 3. The large terraces decrease the short term economic return from a given field of farm land because the increased yield in the terrace area generally doesn't compensate for the land removed from production. PA1 4. The large terraces make it more expensive to farm the land. PA1 5. The natural independence of the American farmer.
A second rainfall control problem is exhibited by near level land. After prolonged heavy rainfall when the soil becomes saturated the excess rainwater all runs to a low spot in the field and forms a large pond. Sometimes these ponds are many acres in extent. If the water from these ponds percolates into the soil too slowly, then crops planted in these areas die and have to be replanted. A further problem with these ponds is that as excess rainwater from a large area percolates into the soil over a small area it leaches a large part of the soil's nutrients down below the root zone of young row crop plants. In this situation the farmer usually has to refertilize as well as replant this area to get a full crop.
The object of this invention is to reduce the foregoing problems of erosion by holding all the rainfall on a field where it falls.
These and other objects of this invention will become apparent from the following disclosure and appended claims.